Safe and efficient drug delivery technologies have been studied for a long time in the treatment using anionic drugs, particularly nucleic acid, and various delivery systems and delivery technologies have been developed. Particularly, delivery technologies using a viral delivery system using adenovius or retrovirus, etc., and a non-viral delivery system using cationic lipids, cationic polymers, etc. have been developed.
However, a technology using a viral delivery system is exposed to a risk such as non-specific immune reaction, etc., and it is known to have a lot of problems in commercialization due to the complex production process. Therefore, recent studies are progressed toward a non-viral delivery system using cationic lipids or cationic polymers to improve the disadvantages. Although the non-viral delivery system has inferior efficiency to the viral delivery system, it has less side effects and the production cost is inexpensive compared with viral delivery system.
Many studies have been conducted on non-viral delivery system used for delivery of nucleic acid, and most representative examples thereof include a complex of cationic lipid and nucleic acid (lipoplex) and a complex of a polycationic polymer and nucleic acid (polyplex). Many studies on the cationic lipid or polycationic polymer have been progressed because it stabilizes anionic drugs by forming a complex by electrostatic interactions with the anionic drug and facilitates intracellular delivery (De Paula D, Bentley M V, Mahato R I, Hydrophobization and bioconjugation for enhanced siRNA delivery and targeting, RNA 13 (2007) 431-56; Gary D, Puri N, Won Y Y, Polymer-based siRNA delivery: Perspectives on the fundamental and phenomenological distinctions from polymer-based DNA delivery, J Control release 121 (2007) 64-73).
However, if cationic lipids or polycationic polymers studied so far are used in an amount required to obtain sufficient effects, serious toxicity, although less than viral delivery system, may be caused and thus it may be improper for the therapeutic use. And, although a lipid-nucleic acid complex which forms a complex through a bond between a cationic lipid and nucleic acid is widely used in a cell line experiment, it does not form a structure that can be stable in blood, and thus it cannot be used in the living body (see U.S. Pat. No. 6,458,382).
A nucleic acid-cationic liposome complex or a cationic liposome comprising nucleic acid, which is one of the non-viral delivery system commonly used to deliver nucleic acid into the cells in the living body, consists of an amphiphilic lipid, a neutral lipid and a fusogenic lipid, etc., and nucleic acid is attached to the outside of the liposome by electrostatic bond or captured inside (US2003-0073640, WO2005/007196, US2006-0240093). Specifically, WO2005/007196 and US2006-0240093 disclose a nucleic acid-lipid particle, comprising a siRNA, a cationic lipid, a non-cationic lipid and a conjugated lipid that inhibits aggregation of particles selected from the group consisting of a polyethyleneglycol (PEG)-lipid conjugate, a polyamide (ATTA)-lipid conjugate, and combinations thereof. However, the liposome delivery system may be easily captured by reticuloendothelial system (RES) and exhibit side effects with significant toxicity, and thus, it may not be appropriate for systemic application. And, another non-viral delivery system commonly used includes a cationic polymer, and a polycationic polymer including multivalent cationic charge per a polymer is predominantly used therefore. Particularly, commonly used polymer is polycationic polyethyleneimine (PEI), and the polycationic polymer binds with nucleic acid material by electrostatic interaction to form a nucleic acid-polymer complex thereby forming a nanoparticle. However, the polycationic polymer such as polyethyleneimine promotes apoptosis, and it is known that cytotoxicity increases as the molecular weight and the degree of branching of the polymer increase. Although polycationic polymers with low molecular weight are known to have low cytotoxicity, they cannot form an effective complex due to low charge density of the polymer, and thus, they cannot show the sufficient intracellular delivery and the sufficient stability in blood.
Therefore, it is required to develop an anionic drug delivery technology using the minimal amount of cationic polymer or cationic lipid to decrease toxicity, which is stable in blood and body fluid, and enables intracellular delivery to obtain sufficient effects. The delivery system using the nucleic acid material directly conjugated with a lipid or a polymer is being studied, but if a lipid or a polymer is directly conjugated with nucleic acid material, there are difficulties in terms of conjugation efficiency or quality control.
Meanwhile, there have been various attempts to use amphiphilic block copolymer as a drug delivery system that can solubilize a poorly water-soluble drug by forming a polymeric micelle and stabilize a poorly water-soluble drug in an aqueous solution (Korean Registered Patent No. 08180334). However, since the amphiphilic block copolymer cannot enclose hydrophilic drug such as nucleic acid in the polymeric micelle, it is not suitable for delivery of anionic drug including nucleic acid.
Meanwhile, many diseases result from the overexpression of disease genes or the expression of mutated genes. Since siRNA (short interfering RNA) inhibits the expression of specific genes in a sequence specific manner, it is highlighted as a therapeutic nucleotide drug. Particularly, siRNA is expected to overcome the problems of the antisense nucleotide or ribozyme because siRNA has more potency and more accurate gene selectivity compared with the antisense nucleotide or ribozyme. The siRNA is a short double-stranded RNA molecule and the number of nucleotides in each strand ranges from 15 to 30, and it inhibits the expression of corresponding gene by cleaving mRNA of gene with a sequence complementary thereto (McManus and Sharp, Nature Rev. Genet. 3:737 (2002); Elbashir, et al., Genes Dev. 15:188 (2001).
However, despite these advantages, siRNA is known to be rapidly degraded by nuclease in blood and rapidly excreted from the body through a kidney. It is also known that siRNA cannot easily pass a cell membrane because it is strongly negatively charged. Therefore, to use siRNA as a therapeutic agent, it is required to develop a delivery system that may stabilize siRNA in blood, may efficiently deliver it into target cells, and does not show toxicity.